The invention relates to xerography and more specifically to a novel photosensitive member and a method of making such a member.
The art of xerography involves the use of a photosensitive element or plate containing a photoconductive insulating layer which is usually first uniformly electrostatically charged in order to sensitize its surface. The plate is then exposed to an image of activating electromagnetic radiation such as light, x-ray, or the like, which selectively dissipates the charge in the exposed areas of the photoconductive insulator while leaving behind a latent electrostatic image in the non-exposed areas. This latent electrostatic image may then be developed and made visible by depositing finely divided electroscopic marking particles on the surface of the photoconductive layer. This concept was originally disclosed by Carlson in U.S. Pat. No. 2,297,691, and is further amplified and described by many related patents in the field.
One type of photoconductor used in xerography is illustrated by U.S. Pat. No. 3,121,006 to Middleton and Reynolds which describes a number of binder layers comprising finely divided particles of photoconductive inorganic compound dispersed in an organic electrically insulating resin binder. It has been found that structures of the Middleton et al type must use a substantially continuous particle-to-particle contact for the photoconductive material throughout the layer in order to permit the charge dissipation required for cyclic operations. With uniform photoconductor dispersions, relatively high volume concentrations of photoconductor up to about 50 percent or more by volume is usually necessary in order to obtain sufficient photoconductor particle-to-particle contact for rapid discharge. It has been found, however, that high photoconductor loadings in binder layers of this type result in the physical continuity of the resin being destroyed and thereby significantly reduce the mechanical properties of the binder layer. Layers with high photoconductor loadings are often characterized by a brittle binder layer having little or no flexibility. On the other hand, when the photoconductor concentration is reduced appreciably below about 50 percent by volume, the discharge rate is reduced, making high speed cyclic or repeated imaging difficult or almost impossible.
In U.S. Pat. No. 3,787,208 to R. N. Jones, the above problems of high photoconductor loading are obviated by a novel xerographic photoreceptor which includes a binder layer which comprises photoconductive particles dispersed in a controlled geometry in an insulating resin matrix. More specifically, substantially all of the photoconductive particles, which are present in a concentration of 1 to 25 percent by volume, are in the form of a plurality of continuous photoconductive paths through the thickness of the binder layer.
The present invention is directed to overcoming the above problems noted in the prior art, and to provide a novel method of making a photoconductive or charge transport layer having a controlled geometry analogous to that set forth in U.S. Pat. No. 3,787,208.